Hi Roy.

05-Oct-03 04:58:54, Roy J. Tellason wrote to Jasen Betts


 RJT> Jasen Betts wrote in a message to Roy J. Tellason:

 PR>>> I know a lot of interfaces have cheated, but RS-232 is supposed
 PR>>> to be +v to -v, v=5 to 15v or so.

 RJT>> I think that's about the only thing that uses the -12 supply any
 RJT>> more,

 JB>> I've got a VGA card here that doesn't produce a usable signal
 JB>> without -12V

 RJT> Oh?  News to me,  but then a lot of hardware surprises me these
 RJT> days.

 RJT>> and even there,  the task of generating a few mA of -12 with a
 RJT>> chip is real easy these days,  has been for a number of years...
 RJT>>   See "max-232" and similar chips

 JB>> yeah, they produce about -9.5 which is close enough I guess.,

 RJT> Eh?  I didn't know that they produced any specific voltage,
 RJT> guess it's been too long since I looked at the data sheets for
 RJT> any of that sort of stuff.

max-232 uses a diode pump (or similar) based around two external capacitors
to pump the +5 up to about 10V  and invert it for the negative rail, I
expect there's some losses involved so I guessed 9.5, whatever it is really
it'll be less than 10V

 RJT> I have one of their catalogs on cdrom,  but it gives you the data in
 RJT> pdf format, which I find inconvenient,  so I don't refer to it often

I have only a third party app note.

 -=> Bye <=-

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